ELI5: Explain Like I'm 5

Charley horse

A charley horse is when your muscle suddenly squeezes really tight and it feels really painful. It can happen when you're playing a sport or just walking around. It's like your muscle is cramping up and won't let go. Sometimes, it feels like a big bump in your leg because the muscle is so tight. Stretching and massaging the muscle can help make it feel better.